You know that you can do a sample memory expansion for the RZ-1, exactly the same as the sample expansion I did on my SK-8. I expanded my SK-8 from 4 samples (just like the RZ) to 128 samples! That sample RAM chip you pointed out can be taken out and replaced by a much bigger capacity RAM chip. The expansion won't give you longer sample times, however, just more samples of the RZ's standard sample times. For the RZ, it will give you 128 banks of the 4 samples = 512 samples, at the push of a button!!
According to the datasheets that I have, the chips labelled " D4364-15L" are the RAM chips, which are 8 x 8kb SRAM chips. I presume one is the sample RAM, and the other is the song/pattern RAM. You could expand both, if you wanted, and have 128x more songs and patterns!
I have attached the expansion instructions for my SK-8, which should be similar for the RZ-1. The SK-8 expands by 32x with this chip, but because the RZ's chip is 4x smaller than the SK-8, it will give you 128x sample expansion, which with 4 samples in the RZ, will give 512 samples!!
Also, you can buy the RZ-1 service manual here, which will tell you everything you need to know about the RZ-1's innards. Essential reading for serious circuitbenders! Email them for a price:
http://www.wdgreenhill.com/manu/casio.htmCheers, Graham